python – TechArt 3D

OpenMaya Callbacks instead of Maya ScriptJobs

Whenever you want something to happen when your selection in Maya changes, the first thing that comes into your mind might be Maya ScriptJobs. However I find them very slow and not reliable, especially since they are wrapped in mel. Better use a callback from OpenMaya’s messaging system. This is how you do it: You will have to create a function that is called every time the selection changes. Make it run fast and with lots of error checking to avoid making your tool too slow. In your function, get the selection and evaluate what you want to do with it. The function could look something like this:

from maya import OpenMaya

#function to execute when selection changes
def maya_selection_changed(*args, **kwargs):
    try:
        sel = OpenMaya.MSelectionList()
        OpenMaya.MGlobal.getActiveSelectionList(sel)

        selection_iter = OpenMaya.MItSelectionList(sel)
        obj = OpenMaya.MObject()
        # Loop though iterator objects
        while not selection_iter.isDone():
            # Now we can do anything with each of selected objects.
            # In this example lets just print path to iterating objects.
            selection_iter.getDependNode(obj)
            dagPath = OpenMaya.MDagPath.getAPathTo(obj)
            print dir(dagPath)
            print dagPath.fullPathName()
            print dagPath.partialPathName()
            #print dir(dagPath)
            selection_iter.next()

    except RuntimeError, err:
        print err

from maya import OpenMaya

#function to execute when selection changes

def maya_selection_changed(*args, **kwargs):

try:

sel = OpenMaya.MSelectionList()

OpenMaya.MGlobal.getActiveSelectionList(sel)

selection_iter = OpenMaya.MItSelectionList(sel)

obj = OpenMaya.MObject()

# Loop though iterator objects

while not selection_iter.isDone():

# Now we can do anything with each of selected objects.

# In this example lets just print path to iterating objects.

selection_iter.getDependNode(obj)

dagPath = OpenMaya.MDagPath.getAPathTo(obj)

print dir(dagPath)

print dagPath.fullPathName()

print dagPath.partialPathName()

#print dir(dagPath)

selection_iter.next()

except RuntimeError, err:

print err

Don’t worry, you don’t have to use maya API but you can use pymel or even maya.cmds instead. In my example I just print the names of the selected nodes however I would avoid any prints as they are slowing down […]

Maya Python

Modify File References before they are loaded

When working on multiple projects you might want to use assets from other projects. Very often a file referencing pipeline makes this difficult though as Maya stores file references with absolute paths when you are not using Maya projects. To avoid this you can hijack the Referencing procedure with a callback.

MSceneMessage.addCheckFileCallback

1	MSceneMessage.addCheckFileCallback

The callback triggers any function you define. In the function you have access to the file path of the reference to do some checks and you can cancel the loading of the reference or manipulate the path to your liking. Create a function somewhere in your pipeline. Your function needs 3 parameters: parameter 1 is the return code (a boolean to approve or cancel the reference load operation) parameter 2 is the file object which holds the path and file information parameter 3 is client data which you can pass in to your function from the callback

def callbackFunction(retCode, fileObject, clientData):
    # printing the original file path
    print "Original file path %s" % fileObject.rawFullName()

    # create a variable for the new file path
    # maybe create some logic for that or even a condition whether to
    # manipulate the path or keep the existing one
    newFilePath = "C:/tmp/newFile.ma"

    # set the file path to be loaded if you want to modify it
    fileObject.setRawFullName(newFilePath)

    # here you can define whether the file should be loaded or
    # whether the reference should be skipped
    OpenMaya.MScriptUtil.setBool(retCode, True)

def callbackFunction(retCode, fileObject, clientData):

# printing the original file path

print "Original file path %s" % fileObject.rawFullName()

# create a variable for the new file path

# maybe create some logic for that or even a condition whether to

# manipulate the path or keep the existing one

newFilePath = "C:/tmp/newFile.ma"

# set the file path to be loaded if you want to modify it

fileObject.setRawFullName(newFilePath)

# here you can define whether the file should be loaded or

# whether the reference should be skipped

OpenMaya.MScriptUtil.setBool(retCode, True)

[…]

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Hello world – again :)

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